The present disclosure generally relates to a method for producing a phenol stream with reduced by-products. More particularly the present invention relates to a two-step continuous method for producing a phenol stream with reduced by-products.
The cleavage reaction of cumene hydroperoxide (CHP) in the manufacture of phenol and acetone from cumene is well known. Today most modern CHP cleavage processes are carried out in a continuous flow manner and utilize the so-called “2-stage cleavage process”, which provides the best economics because, in addition to making phenol and acetone from CHP, it recovers cumene value from the by-product DMBA formed in the prior cumene oxidation step. Such prior art 2-stage cleavage processes are described in U.S. Pat. Nos. 6,307,112, 6,225,513, 6,201,157, 6,057,483, 5,998,677, 5,530,166, 54,63,136, 5,430,200, 5,371,305, 5,254,751, and 4,358,618.
In the 1st cleavage stage, a technical grade CHP feed is predominantly decomposed with an acid to form phenol and acetone in equal molar amounts, however, at the same time the reaction conditions of the 1st stage are carefully controlled to allow a small amount of CHP to remain undecomposed so that it can react with the DMBA in the incoming feed stream to produce dicumylperoxide (DCP). This 1st stage process can utilize a constant boiling or acetone-refluxing type reactor design for the CHP cleavage reaction, or it can utilize a multiplicity of non-boiling CHP decomposers.
In the 2nd stage of the cleavage process, the DCP that was generated in the 1st stage is decomposed under controlled conditions to form acetone, phenol, and alpha-methylstryrene (AMS) in high yield with little tar formation. The AMS formed here from the DCP can later be easily converted to cumene via hydrogenation, and recycled for reuse. Thus, the overall effect is that the DMBA by-product is recovered as valuable cumene and prevented from converting to tarry by-product wastes.
To encourage the formation of DCP in the 1st stage, prior art processes generally use excess acetone to retard the acidic decomposition of CHP and allow it to accumulate in small part. The amounts of additional acetone described in the prior art as effective are about 10–40% excess over the amount of “in-situ” acetone generated during the CHP decomposition reaction. Thus, the acetone:phenol molar ratio is typically maintained at 1.1:1 to 1.5:1 during the cleavage reaction medium.
Although extra acetone addition can be an effective method for inhibiting the CHP decomposition reaction and enhancing DCP formation, such a cleavage process operating with a high acetone:phenol ratio is subject to the disadvantage of forming increased levels of other harmful “carbonyl-type” by-products such as hydroxyacetone (also known as HA or acetol) and mesityl oxide (MO).
Moreover, as a result of the carbonyl impurities formed during cleavage, the resulting phenol and acetone products have to be separated from these undesirable by-products and impurities using energy intensive processes. For example, the presence of acetol impurities in the phenol product renders quality unacceptable for many end-use applications, such as in the production of bisphenol-A, diphenyl carbonate, and polycarbonate. Furthermore, the phenol product that contains acetol impurities tends to discolor upon aging, or during subsequent reactions, such as during sulfonation and chlorination reactions.
The hydroxyacetone impurity has proven to be particularly difficult to remove from the phenol product in a downstream process since it co-distills at a similar temperature as phenol during thermal separation processes, e.g., rectification processes. Because of this, current thermal separation processes are generally ineffective at purifying the phenol product to remove the acetol impurity. As a result various chemical removal methods are commonly used in the downstream phenol process for carbonyls removal. This includes treatment with various acids, bases, ion exchange resins, zeolites, etc. All of these approaches are costly, requiring expensive reagents and additional equipment.
To date little or no progress has been made in reducing the acetol by-product amount in the phenol process at its point of generation, that is the CHP cleavage step. Reducing the amount of hydroxyacetone and other carbonyls early in the process at the CHP cleavage process would greatly simplify the downstream purification steps, reducing investment and energy consumption.
Accordingly, there is a need in the art for an improved continuous process for producing phenol from CHP that does not produce the harmful “carbonyl-type” by-products that is obtained from the use of excess acetone during the cleavage reaction. Such a process would desirably be a more economically favorable method for producing the purified phenol product.